Synthesis and characterization of exfoliated poly(styrene‐co‐methyl methacrylate) nanocomposite via miniemulsion atom transfer radical polymerization: an activators generated by electron transfer approach

Exfoliated poly(styrene‐co‐methyl methacrylate) nanocomposites were synthesized using activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP). Miniemulsion polymerization was used for its abundant advantages to encapsulate inorganic materials and eliminate organic solvents from products for environmentally friendly purposes. Cetyltrimethylammonium bromide (CTAB) as a cationic surfactant, which is an effective surfactant at higher temperatures, was used to stabilize the miniemulsion system. Successful miniemulsion AGET ATRP was carried out by using 4,4'‐dinonyl‐2,2'‐bipyridine (dNbPy) as a hydrophobic ligand. Formation of monodispersed droplets and particles with sizes in the range of 200nm was examined by dynamic light scattering (DLS). Conversion and molecular weight study were also carried out using gravimetry and gel permeation chromatography, respectively. By adding clay content, a decrease in the conversion and molecular weight of the nanocomposites are observed. However, an increase in the PDI values of nanocomposites was observed by the addition of nanoclay content. Thermogravimetric analysis results demonstrate that thermal stability of all the nanocomposites in comparison with the neat copolymer increases. Differential scanning calorimetry results show that T_g decreases by increasing clay content. Monodisperse distribution of spherical shape particles with sizes in the range of ∼ 200 nm was demonstrated by using scanning electron microscopy images of nanocomposite containing 1 wt% of nanoclay, which is more compiled with DLS results. Transmission electron microscopy results shows well‐dispersed exfoliated clay layers in the polymer matrix of PSMNM 1, which is coincidence with X‐ray diffraction data. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Detection of arsenic agents by polyhydroxamic acid

Arsenic agents are among the most destructive and fatal factors that exist in the environment, chemical agents, medicines, toxics, pesticides, etc., and working with these compounds is too limited and difficult due to their high toxicity. These deadly, dangerous, and weakening toxins are consumed for a large variety of purposes in the military industries. So measurement and identification of them are of great necessity. In this research work, acryl carbohydroxamic acid monomer was first prepared from acrylamide and then polymerized under radical conditions in the presence of azobisisobutyronitrile as an initiator. The produced polyhydroxamic acid (PHA) has antibacterial and anticancer properties as well as high complex‐forming properties with transition elements. By using the chelating properties of PHA, we took steps to identify arsenic agents such as trichloroarsine, dichloroethylarsine, and lewisites (I, II, III). This polymer, possessing unique properties, measures well the arsenic of low concentrations, lower than 10 ppm, existing in the samples within a very short time (a few seconds). We will also be able to perform qualitative assessments on it through instrumental methods or titration, if required. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of tailor‐made polystyrene nanocomposite with mixed clay‐anchored and free chains via atom transfer radical polymerization

Tailor‐made polystyrene nanocomposite with mixed free and clay‐attached polystyrene chains was synthesized using atom transfer radical polymerization. Vinylbenzyl trimethylammonium chloride having a double bond, which could be incorporated into polystyrene chains by a grafting through process, was used as a nanoclay modifier. Conversion and molecular weight evaluation was carried out using gas chromatography and gel permeation chromatography, respectively. The thermogravimetric analysis results confirmed the elevated thermal stability of the nanocomposites in comparison with the neat polystyrene sample. Additionally, the T_g increases by clay loading was confirmed by differential scanning calorimetry (DSC). The difference in the degradation temperature of C? Br bond in attached and free polystyrene chains was well revealed in DSC thermograms. Finally, a lower clay loading resulted in an exfoliated structure as proved by X‐ray diffraction and transmission electron microscopy results. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Investigation of effective dimensionless numbers on initiation of instability in combustion of moisty organic dust简

In this work, the effect of various effective dimensionless numbers and moisture contents on initiation of instability in combustion of moisty organic dust is calculated. To have reliable model, effect of thermal radiation is taken into account. One- dimensional flame structure is divided into three zones： preheat zone, reaction zone and post-flame zone. To investigate pulsating characteristics of flame, governing equations are rewritten in dimensionless space-time （（, r/, ~） coordinates. By solving these newly achieved governing equations and combining them, which is completely discussed in body of article, a new expression is obtained. By solving this equation, it is possible to predict initiation of instability in organic dust flame. According to the obtained results by increasing Lewis number, threshold of instability happens sooner. On the other hand, pulsating is postponed by increasing Damk6hler number, pyrolysis temperature or moisture content. Also, by considering thermal radiation effect, burning velocity predicted by our model is closer to experimental results.     

Selective harmonic elimination method for wide range of modulation indexes in multilevel inverters using ICA

Selective harmonic elimination（SHE） in multilevel inverters is an intricate optimization problem that involves a set of nonlinear transcendental equations which have multiple local minima. A new advanced objective function with proper weighting is proposed and also its efficiency is compared with the objective function which is more similar to the proposed one. To enhance the ability of the SHE in eliminating high number of selected harmonics, at each level of the output voltage, one slot is created. The SHE problem is solved by imperialist competitive algorithm（ICA）. The conventional SHE methods cannot eliminate the selected harmonics and satisfy the fundamental component in some ranges of modulation indexes. So, to surmount the SHE defect, a DC-DC converter is applied. Theoretical results are substantiated by simulations and experimental results for a 9-level multilevel inverter. The obtained results illustrate that the proposed method successfully minimizes a large number of identified harmonics which consequences very low total harmonic distortion of output voltage.     

Genetic Deficiency and Pharmacological Stabilization of Mast Cells Ameliorate Pressure Overload-Induced Maladaptive Right Ventricular Remodeling in Mice

Although the response of the right ventricle (RV) to the increased afterload is an important determinant of the patient outcome, very little is known about the underlying mechanisms. Mast cells have been implicated in the pathogenesis of left ventricular maladaptive remodeling and failure. However, the role of mast cells in RV remodeling remains unexplored. We subjected mast cell-deficient WBB6F1-KitW/W-v (Kit^W/Kit^W-v) mice and their mast cell-sufficient littermate controls (MC^+/+) to pulmonary artery banding (PAB). PAB led to RV dilatation, extensive myocardial fibrosis, and RV dysfunction in MC^+/+ mice. In PAB Kit^W/Kit^W-v mice, RV remodeling was characterized by minimal RV chamber dilatation and preserved RV function. We further administered to C57Bl/6J mice either placebo or cromolyn treatment starting from day 1 or 7 days after PAB surgery to test whether mast cells stabilizing drugs can prevent or reverse maladaptive RV remodeling. Both preventive and therapeutic cromolyn applications significantly attenuated RV dilatation and improved RV function. Our study establishes a previously undescribed role of mast cells in pressure overload-induced adverse RV remodeling. Mast cells may thus represent an interesting target for the development of a new therapeutic approach directed specifically at the heart.     

Unique microstructure analysis of ethylene-propylene copolymer synthesized using catalytic system based on α-diimine nickel complexes: a comparative study by 13C NMR technique

The microstructure of rubber-like ethylene-propylene copolymer (MN4) produced by a mixed nickel-based system (MN) containing catalysts of dibromo[N,N′-bis(2,6-diisopropylphenyl)-2,3-butanediimine]nickel(II) n1 and dibromo[N,N′-(phenanthrene-9,10-diylidene)bis(2,6-diisopropylaniline)]nickel(II) n2 was determined by ¹³C NMR technique. Sequences distribution of ethylene (E), propylene (P), EP, inverted propylene and uninterrupted methylene and also methylene number-average sequence lengths for the copolymer (MN4) were estimated. The results obtained from the MN4 EP copolymer were compared with reported copolymers which had been synthesized using constrained geometry catalyst (CGC) and vanadium-based Ziegler-Natta catalyst. The results demonstrated that the MN4 EP copolymer had fewer alternating comonomer sequences than ethylene-propylene elastomers obtained by CGC and vanadium-based (V) catalysts. A large number of the inversion structures (66 %) and high mole percent of sequences containing a long branch (3.2 mol%) were also observed in unique microstructure of the copolymer (MN4).     

Quantum chemical studies on molecular conformations,energetic and intramolecular hydrogen bonding in ground and electronic excited state of (thioxosilyl) ethyleneselenol

In this work, a conformational analysis of (thioxosilyl) ethyleneselenol was performed using several computational methods, including density-functional theory (DFT) (B3LYP), MP2 and G2MP2. Harmonic vibrational frequencies were estimated at the same levels to confirm the nature of the stationary points found and also to account for the zero point vibrational energy correction. MES-1 and TES-1 conformers exhibit hydrogen bonding. This feature, although is not the dominant factor in the stability of conformers, appears to be of foremost importance to define the geometry of the molecule. Two intramolecular hydrogen bonds established between the polar groups were identified by the structural geometric parameters. These involved the thiol and selenol functional groups and were identified and characterized by the frequency shift in their stretching vibration modes. Furthermore, the excited-state properties of intramolecular hydrogen bonding have been investigated theoretically using the time-dependent DFT method. The influence of the solvent on the stability order of conformers and the strength of intramolecular hydrogen bonding was considered using the PCM (polarizable continuum model), SCI-PCM (self consistent isodensity-polarizable continuum model) and IEF-PCM (integral equation formalism-polarizable continuum model) methods. The “atoms in molecules” theory of Bader was used to analyze critical points and to study the nature of hydrogen bond in these systems. Natural bond orbital (NBO) analysis was also performed for better understanding the nature of intramolecular interactions. The calculated highest occupiedmolecular orbital and lowest unoccupied molecular orbital energies show that charge transfer occur within the molecule. Further verification of the obtained transition state structures was implemented via intrinsic reaction coordinate analysis. Calculations of the ¹H NMR chemical shift at the GIAO/B3LYP/6–311++G** level of theory are also presented.     

Highly efficient synthesis of benzopyranopyridines via ZrP2O7 nanoparticles catalyzed multicomponent reactions of salicylaldehydes with malononitrile and thiols

ZrP₂O₇ nanoparticles as an efficient catalyst have been used for the preparation of benzopyrano[2,3-b]pyridines from the four-component condensation reaction of salicylalde-hydes, thiols, and 2 equiv. of malononitrile under reflux conditions in ethanol in excellent yields and short reaction times.